1. Field of the Invention
The present invention relates to a lighting device such as the combination lamp provided with a lens longer in the horizontal direction thereof and attached as a part to form the exterior of vehicles.
2. Description of the Prior Art
In the case of the rear combination lamp having a lens longer in the horizontal direction thereof, for example, the tail stop lamp which emits red light, the turn signal lamp which emits orange light, and the backup lamp which emits white light are combined with one another to form the rear combination lamp or lighting device. The tail stop lamp is a combination of the tail lamp which informs persons behind of the presence of a vehicle at night and the stop lamp which emits light when the vehicle is braked. The turn signal lamp serves to tell the change of that lane on which the vehicle is running and the backup lamp serves to illuminate behind and tell that the vehicle is to move backward.
In the case of this lighting device, however, there arises the problem of false lighting. This is a phenomenon seen in the daytime when sun light enters into the lighting device and reflected by the prism on the backside of the lens or reflector in the lighting device. The lighting device is seen at this time as if it were lit. This phenomenon is also sometimes seen at night when the lighting device is illuminated by headlamps of other vehicles.
When this false lighting is seen at the tail stop lamp, for example, there is a danger that the vehicle behind puts on an emergency brake, with the driven thinking that the preceding vehicle had been braked, to thereby make persons travelling in the following vehicle to fear a collision. This sudden braking can also cause the vehicle to be hit from behind.
In order to prevent this false lighting, plural stripes which serve to shield light entering into the lighting device from outside are arranged on the front or back of the lens in the horizontal direction thereof, but these light shielding stripes uniformly formed on the whole front or back surface of the lens reduce the light distributing capacity of the lighting device.
When the light shielding stripes are to be formed directly on the front or back of the lens, as described above, it is necessary that every lens be processed to have these light shielding stripes thereon. This takes time and makes the cost high.
Further, a trend has arisen these days that the lighting devices are made as thin as possible. When made so thin, the lighting devices can become lighter in weight and lower in material cost. In the case where the rear combination lamp is made so thin according to this trend, the trunk room can have a larger volume. When the lighting devices are made thin like this, however, they can look not three-dimensional but flat and this gives no satisfied feeling to persons who see them from their lens side. This also cannot satisfy those persons who want to possess products of high grade.
The applicant of the present invention has proposed in Japanese Patent Application No. 62-93290 a technique in which a transparent sheet is bonded to the surface of an inner lens and in which graduations are applied to the transparent sheet to let the lamp have three-dimensional appearance even when it is made thin. This technique enables the false lighting to be prevented without any process added to the lens.
In the case where the transparent sheet is bonded to the surface of the inner lens, however, the sun light entering into the lighting device from outside may be reflected by the surface of the transparent sheet because this sheet is usually made of synthetic resin and has a brilliant surface. When the sheet is even a little swelled, therefore, the sun light reflected looks like a striped pattern, thereby making it difficult to recognize the lighting device itself.
Although the above-mentioned Japanese Patent Application No. 62-93290 does not disclose a concrete technique of bonding the transparent sheet to the surface of the inner lens, it is preferable that the bonding process can be achieved reliably, easily and quickly.